Many of us have our own little rituals before going to bed. Some of us use skincare products, drink a warm glass of milk, or even read a book before we fall asleep. Certain species of the reef-dwelling parrotfish have a strange (and rather icky-sounding) bedtime habit, though: They blow out a large bubble of their own mucus and sleep inside it.
Special glands in these fishes’ gills secrete mucus, forming a cocoon that covers their bodies. For a long time, marine scientists weren’t sure exactly why a number of parrotfish and wrasse species could do this. They had many theories, though, including the cocoon serving as a shield against dust or sunlight, an early warning system, or protection against moray eels and other predators.
Creating a cocoon requires less than an hour of the parrotfish’s time, and about 2.5 percent of its energy. Still, it’s a relatively small price to pay for a decent night’s sleep.
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